Terrie, Leaders & enders is what Bonnie Hunter does/calls the scrap of fabric that you put under the needle when you come to the end of a length of sewing blocks so that you don't have a long end of thread and it helps to avoid the 'birds nest'' the appears on the underside when you start again. If you are super organised
you have a box of pieces already cut - say squares for a 4 patch - sitting next to the machine and you stitch them instead of using a thread saver. Bonnie Hunter's latest leader & ender project has been tumblers, but any fairly basic block will do, and you end up making a second quilt whilst concentrating on the main one. In the past she has made a load of 9 patches, pinned them in sets of 10 and put them to one side to mature for a few years, then when faced with an urgent baby quilt requirement, pulled them out, sashed them and 'Bob's your uncle' instant quilt!
I have another leader & ender project that is basically any scrap that can be cut 2 1/2" but is too short to be square, is tossed into the box and then they are sewn into pairs,& then 4's etc any old how and I will end up with a multi-coloured 'jelly roll' for something.